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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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NASA NTRS1987

Numerical models of star formation in X-ray cluster cooling flows

A grid of numerical models is used here to study how accretion flows are affected by star formation. The observables associated with these models are investigated, presenting their X-ray surface brightness profiles. An X-ray diagnostic is searched for that, in the absence of spatially resolved X-ray spectral data, can be an unambiguous indicator for ongoing star formation in cooling flows. The spatial distributions of newly formed stars are presented and compared to profiles of the accreting galaxy in each model. Whether the accretion population can form the luminous parts of the accreting galaxy or whether it forms a dark component is considered.

White, Raymond E., III↗
NASA NTRS1998

Chemical Abundances of Planetary Nebulae in the Bulge and Disk of M31

We derive abundances and central star parameters for 15 planetary nebulae (PNe) in M31: 12 in the bulge and 3 in a disk field 14 kpc from the nucleus. No single abundance value characterizes the bulge stars: although the median abundances of the sample are similar to those seen for PNe in the LMC, the distribution of abundances is several times broader, spanning over 1 decade. None of the PNe in our sample approach the super metal-rich ([Fe/H] approximately 0.25) expectations for the bulge of M31, although a few PNe in the sample of Stasinska, Richer, & Mc Call (1998) come close. This [O/H] vs [Fe/H] discrepancy is likely due to a combination of factors, including an inability of metal-rich stars to produce bright PNe, a luminosity selection effect, and an abundance gradient in the bulge of M31. We show that PNe that are near the bright limit of the [O III] lambda.5007 planetary nebula luminosity function (PNLF) span nearly a decade in oxygen abundance, and thus, support the use of the PNLF for deriving distances to galaxies (Jacoby 1996) with differing metallicities. We also identify a correlation between central star mass and PN dust formation that partially alleviates any dependence of the PNLF maximum magnitude on population age. Additionally, we identify a spatially compact group of 5 PNe having unusually high O/H; this subgroup may arise from a recent merger, but velocity information is needed to assess the true nature of the objects.

Jacoby, George H.↗
NASA NTRS2007

The UDF05 Follow-up of the HUDF: I. The Faint-End Slope of the Lyman-Break Galaxy Population at zeta approx. 5

We present the UDF05 project, a HST Large Program of deep ACS (F606W, F775W, F850LP, and NICMOS (Fll0W, Fl60W) imaging of three fields, two of which coincide with the NICP1-4 NICMOS parallel observations of the Hubble Ultra Deep Field (HUDF). In this first paper we use the ACS data for the NICP12 field, as well as the original HUDF ACS data, to measure the UV Luminosity Function (LF) of z approximately 5 Lyman Break Galaxies (LBGs) down to very faint levels. Specifically, based on a V - i, i - z selection criterion, we identify a sample of 101 and 133 candidate z approximately 5 galaxies down to z(sub 850) = 28.5 and 29.25 magnitudes in the NICP12 field and in the HUDF, respectively. Using an extensive set of Monte Carlo simulations we derive corrections for observational biases and selection effects, and construct the rest-frame 1400 Angstroms LBG LF over the range M(sub 1400) = [-22.2, -17.1], i.e. down to approximately 0.04 L(sub *) at z = 5. We show that: (i) Different assumptions for the SED distribution of the LBG population, dust properties and intergalactic absorption result in a 25% variation in the number density of LBGs at z = 5 (ii) Under consistent assumptions for dust properties and intergalactic absorption, the HUDF is about 30% under-dense in z = 5 LBGs relative to the NICP12 field, a variation which is well explained by cosmic variance; (iii) The faint-end slope of the LF is independent of the specific assumptions for the input physical parameters, and has a value of alpha approximately -1.6, similar to the faint-end slope of the LF that has been measured for LBGs at z = 3 and z = 6. Our study therefore supports no variation in the faint-end of the LBG LF over the whole redshift range z = 3 to z = 6. The comparison with theoretical predictions suggests that (a,) the majority of the stars in the z = 5 LBG population are produced with a Top-Heavy IMF in merger-driven starbursts, and that (b) possibly, either the fraction of stellar mass produced in starburst, or the fraction of high mass stars in the bursts is increased towards the bright end of the LF.

Oesch, P. A.↗
NASA NTRS1992

The H II regions of the galaxy M101

The physical properties and composition of the H II region population of the spiral galaxy M101 (NGC 5457) were examined using spectrophotometrically calibrated CCD imagery of two overlapping 16-arcmin fields in the M101, in which individual H II regions were identified and mapped using an automated algorithm. The characteristics obtained for the H II region population of M101 include the H II region luminosity function and radial variations in extinction; the forbidden O III line/H-beta, O/H, and forbidden S II line/H-alpha ratios; the ionization parameter U; and the numbers of ionizing photons. Global variations of physical properties of the H II regions in M101 are compared to model expectations derived for other galaxies. The evident star formation in the M101 galaxy is discussed.

Scowen, P. A.↗
NASA NTRS1990

The oxygen emission lines in Wolf-Rayet spectra

The statistical equilibrium of oxygen in the line-emitting regions of WR stars is studied using the one-representative point theory of Castor and van Blerkom (1970) for a wider range of the radiation temperature, electron temperature, and electron density. Radiative processes, collisional processes, and electronic recombination are studied for a 59-level model atom. The level populations depart by large factors from those expected for LTE at the electron temperature and electron density. When the parameters have the values found previously by Bhatia and Underhill to be representative for WR stars, the oxygen atoms are strongly concentrated in the lower levels of O(2+), O(3+), and O(4+). The predicted relative energies in typical lines of O III, O IV, and O V for a solar abundance ratio of O to H are compatible with what is observed in WC and WN spectra.

Bhatia, A. K.↗
NASA NTRS2013

High-Resolution Near-Infrared Spectroscopy of an Equivalent Width-Selected Sample of Starbursting Dwarf Galaxies

Spectroscopic observations from the Large Binocular Telescope and the Very Large Telescope reveal kinematically narrow lines (approx. 50 km/s) for a sample of 14 Extreme Emission Line Galaxies (EELGs) at redshifts 1.4 < zeta < 2.3. These measurements imply that the total dynamical masses of these systems are low ( 3 × 10(exp 9) M). Their large [O III]5007 equivalent widths (500 − 1100 A) and faint blue continuum emission imply young ages of 10−100 Myr and stellar masses of 10(exp 8)−10(exp 9) M, confirming the presence of a violent starburst. The stellar mass formed in this vigorous starburst phase thus represents a large fraction of the total (dynamical) mass, without a significantly massive underlying population of older stars. The occurrence of such intense events in shallow potentials strongly suggests that supernova-driven winds must be of critical importance in the subsequent evolution of these systems.

Spectroscopy↗
NASA NTRS2012

Reconstructing the Gamma-Ray Photon Optical Depth of the Universe To Z Approx. 4 from Multiwavelength Galaxy Survey Data

Reconstructing the Gamma-Ray Photon Optical Depth of the Universe To Z Approx. 4fFrom Multiwavelength Galaxy Survey Data We reconstruct the gamma-ray opacity of the universe out to z approx. < 3–4 using an extensive library of 342 observed galaxy luminosity function (LF) surveys extending to high redshifts .We cover the whole range from UV to mid-IR (0.15–25 micron ) providing for the first time a robust empirical calculation of the gamma gamma optical depth out to several TeV. Here, we use the same database as Helgason et al. where the extragalactic background light was reconstructed from LFs out to 4.5 micron and was shown to recover observed galaxy counts to high accuracy. We extend our earlier library Of LFs to 25micron such that it covers the energy range of pair production with gamma -rays (1) in the entire Fermi/LAT energy range, and (2) at higher TeV energies probed by ground-based Cherenkov telescopes. In the absence of significant contributions to the cosmic diffuse background from unknown populations, such as the putative Population III era sources, the universe appears to be largely transparent to gamma-rays at all Fermi/LAT energies out to z approx.. 2 whereas it becomes opaque to TeV photons already at z approx. < 0.2 and reaching tau approx∼ 10 at z = 1. Comparing with the currently available Fermi/LAT gamma-ray burst and blazar data shows that there is room for significant emissions originating in the first stars era.

galaxies:evolution↗
DOE OSTI2022

Black hole–neutron star mergers: The first mass gap and kilonovae

Observations of X-ray binaries indicate a dearth of compact objects in the mass range from ~2 –5 M ⊙ . The existence of this (first mass) gap has been used to discriminate between proposed engines behind core-collapse supernovae. From LIGO/Virgo observations of binary compact remnant masses, several candidate first mass gap objects, either neutron stars (NSs) or black holes (BHs), were identified during the O3 science run. Motivated by these new observations, we study the formation of BH-NS mergers in the framework of isolated classical binary evolution, using population synthesis methods to evolve large populations of binary stars (Population I and II) across cosmic time. We present results on the NS to BH mass ratios (q = M NS /M BH ) in merging systems, showing that although systems with a mass ratio as low as q = 0.02 can exist, typically BH-NS systems form with moderate mass ratios q = 0.1 –0.2. If we adopt a delayed supernova engine, we conclude that ~30% of BH-NS mergers may host at least one compact object in the first mass gap (FMG). Even allowing for uncertainties in the processes behind compact object formation, we expect the fraction of BH-NS systems ejecting mass during the merger to be small (from ~0.6 –9%). In our reference model, we assume: (i) the formation of compact objects within the FMG, (ii) natal NS/BH kicks decreased by fallback, (iii) low BH spins due to Tayler-Spruit angular momentum transport in massive stars. We find that ≲1% of BH-NS mergers will have any mass ejection and about the same percentage will produce kilonova bright enough to have a chance of being detected with a large (Subaru-class) 8 m telescope. Interestingly, all these mergers will have both a BH and an NS in the FMG.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1992

Improved calculations for the C III 1907,1909 and Si III 1883,1892 electron density sensitive emission-line ratios, and a comparison with IUE observations

Atomic data are used in conjunction with the statistical equilibrium code of Dufton (1977) to calculate relative C III and Si III level populations, and hence emission-line strengths for a range of electron temperatures and densities. It is assumed that photoexcitation and deexcitaton rates are negligible in comparison with the corresponding collisional rates, that ionization to and recombination from other ionic levels are slow compared with bound-bound rates, and that all transitions are optically thin. The observed values of R1 and R2 for several planetary nebulae and a symbiotic star, measured from high-resolution spectra obtained with the IUE satellite, lead to electron densities that are compatible, and are also in good agreement with those deduced from line ratios in other species.

Keenan, F. P.↗
NASA NTRS1993

Central star formation in early-type galaxies: Images and implications

We are reporting on an on-going study of strong central star-bursts in early type galaxies. These galaxies are brighter than m(pg) = 14.5 and are classified as type SO, SO/a, or Sa in the Uppsala General Catalog. All of them have unusually warm, bright far infrared sources for early-type galaxies, with F(100 microns)/F(60 microns) less than 2.0 and F(60 microns) greater than 2.5 Jy. Much of the infrared emission comes from the central few arcsec. Most of the galaxies were detected at 2380 MHz at Arecibo, with flux densities between 15 and 33 mJy. They have diffuse radio sources with a variety of morphologies, typically a few kpc in extent. Long slit spectra through the nucleus show that all have Balmer absorption lines, signifying a large B or A star population, and (O2) 3727 and Balmer emission lines, consistent with ionization by hot young stars. We have made optical continuum and emission line images of the galaxies to use in combination with the above data to study the causes and evolution of strong central star-bursts in early-type disk systems.

Dressel, L. L.↗
DOE OSTI2023

High-z galaxies with JWST and local analogues – it is not only star formation

ABSTRACT I present an analysis of the JWST NIRSpec data of SMACS 0723 released as Early Release Observations. As part of this three new redshifts are provided, bringing the total of reliable redshifts to 14. I propose a modification to the direct abundance determination method that reduces sensitivity to flux calibration uncertainties by a factor of ∼3 and show that the resulting abundances are in good agreement with Bayesian photoionization models of the rest-frame optical spectrum. I also show that 6355 is most likely a narrow-line active galactic nucleus (AGN) with $M_*\lt 10^9\, \mathrm{M}_\odot$ at z = 7.66 and argue that 10 612 might also have an AGN contribution to its flux through comparison to photoionization models and low-redshift analogues. Under the assumption that the lines come from star formation, I find that the galaxies have gas depletion times of ∼107 yr, comparable to similar galaxies locally. I also identify a population of possibly shock-dominated galaxies at z < 3, whose near-IR emission lines plausibly come nearly all from shocks and discuss their implications. I close with a discussion of the potential for biases in the determination of the mass–metallicity relation using samples defined by detected [O iii]4363 and show using low-z galaxies that this can lead to biases of up to 0.5 dex with a systematic trend with mass.

Brinchmann, Jarle (ORCID:0000000343598797)↗
NASA NTRS2022

The Population of Galactic Centre Filaments – III. Candidate Radio and Stellar Sources

Recent MeerKAT radio continuum observations of the Galactic Centre at 20 cm show a large population of non-thermal radio filaments (NRFs) in the inner few hundred pc of the Galaxy. We have selected a sample of 57 radio sources, mainly compact objects, in the MeerKAT mosaic image that appear to be associated with NRFs. The selected sources are about four times the number of radio point sources associated with filaments than would be expected by random chance. Furthermore, an apparent correlation between bright IR stars and NRFs is inferred from their similar latitude distributions, suggesting that they both co-exist within the same region. To examine if compact radio sources are related to compact IR sources, we have used archival 2MASS, and Spitzer data to make spectral energy distribution of individual stellar sources coincident or close to radio sources. We provide a catalogue of radio and IR sources for future detailed observations to investigate a potential three-way physical association between NRFs, compact radio and IR stellar sources. This association is suggested by models in which NRFs are cometary tails produced by the interaction of a large-scale nuclear outflow with stellar wind bubbles in the Galactic Centre.

plasmas↗
NASA NTRS1993

The evolution of the lithium abundances of solar-type stars. III - The Pleiades

New measurements of lithium in more than 100 Pleiades F, G, and K dwarfs are reported. Abundances are determined from spectrum synthesis fits to the data as well as from use of new covers of growth from the Li 6708-A feature. It is argued that most Late-F and early-G dwarfs in the Pleiades are consistent with the tight N(Li) vs mass relation seen in the Hyades in the same mass range. Most Li-rich stars have abundances at or near the primordial level for Population I, and none exceed that level by a significant amount. At any given color the stars that rotate fast have the most Li and have the strongest chromospheric activity. Ways in which an apparent spread in N(Li) could arise from an intrinsically tight n(Li)-mass relation are considered, and it is concluded that the spread is probably real and is not an artifact of line formation conditions or inhomogeneous atmospheres on the stars.

Soderblom, David R.↗
DOE OSTI2022

Diffstar: a fully parametric physical model for galaxy assembly history

We present Diffstar, a smooth parametric model for the in situ star formation history (SFH) of galaxies. The Diffstar model is distinct from traditional SFH models because it is parametrized directly in terms of basic features of galaxy formation physics. Diffstar includes ingredients for: the halo mass assembly history; the accretion of gas into the dark matter halo; the fraction of gas that is eventually transformed into stars, ϵ ms ; the time-scale over which this transformation occurs, τ cons ; and the possibility that some galaxies will experience a quenching event at time t q , and may subsequently experience rejuvenated star formation. We show that our model is sufficiently flexible to describe the average stellar mass histories of galaxies in both the IllustrisTNG (TNG) and UniverseMachine (UM) simulations with an accuracy of ~0.1 dex across most of cosmic time. We use Diffstar to compare TNG to UM in common physical terms, finding that: (i) star formation in UM is less efficient and burstier relative to TNG; (ii) UM galaxies have longer gas consumption time-scales, relative to TNG; (iii) rejuvenated star formation is ubiquitous in UM, whereas quenched TNG galaxies rarely experience sustained rejuvenation; and (iv) in both simulations, the distributions of ϵ ms , τ cons , and t q share a common characteristic dependence upon halo mass, and present significant correlations with halo assembly history. Finally, we conclude with a discussion of how Diffstar can be used in future applications to fit the SEDs of individual observed galaxies, as well as in forward-modelling applications that populate cosmological simulations with synthetic galaxies.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Determining star formation rates in AGN hosts from strong optical emission lines

ABSTRACT The influence of Active Galactic Nuclei (AGN) on star formation within their host galaxies remains a topic of intense debate. One of the primary challenges in quantifying the star formation rate (SFR) within AGN hosts arises from the prevalent assumption in most methodologies, which attribute gas excitation to young stars alone. However, this assumption does not consider the contribution of the AGN to the ionization of the gas in their environment. To address this issue, we evaluate the use of strong optical emission lines to obtain the SFR surface density ($\Sigma {{\rm SFR_{AGN}}}$) in regions predominantly ionized by an AGN, using a sample of 293 AGN hosts from the MaNGA survey, with SFR measurements available through stellar population fitting. We propose calibrations involving the H$\alpha$ and [O iii]$\lambda$5007 emission lines, which can be used to determine $\Sigma {{\rm SFR_{AGN}}}$, resulting in values consistent with those estimated through stellar population fitting.

de Mellos, Maitê S. Z. (ORCID:0009000821841403)↗
NASA NTRS2013

Confirmation of Small Dynamical and Stellar Masses for Extreme Emission Line Galaxies at z Approx. 2

Spectroscopic observations from the Large Binocular Telescope and the Very Large Telescope reveal kinematically narrow lines (approx. 50 km/s) for a sample of 14 extreme emission line galaxies at redshifts 1.4 < z < 2.3. These measurements imply that the total dynamical masses of these systems are low (< or approx. 3 × 10(exp 9) M). Their large [O III] (lambda)5007 equivalent widths (500-1100 Angstroms) and faint blue continuum emission imply young ages of 10-100 Myr and stellar masses of 10(exp 8)-10(exp 9)M, confirming the presence of a violent starburst. The dynamical masses represent the first such determinations for low-mass galaxies at z > 1. The stellar mass formed in this vigorous starburst phase represents a large fraction of the total (dynamical) mass, without a significantly massive underlying population of older stars. The occurrence of such intense events in shallow potentials strongly suggests that supernova-driven winds must be of critical importance in the subsequent evolution of these systems.

Confirmation↗
NASA NTRS1993

High-resolution study of luminous infrared galaxies. I - The composite nature of the Seyfert 1 galaxy IRAS 20044-6114 (NGC 6860)

The physical conditions in the ionized gas, the stellar population, and the kinematics of the Seyfert 1 galaxy IRAS 20044-6114 (NGC 6860) are studied by high spatial resolution optical imaging and optical and near-IR spectroscopy of this luminous IR source. The broadband images show a compact nucleus, two weak spiral arms, a bar, a bulge, an inner ring, and a possible outer ring. The I-alpha image reveals bright emission-line regions associated with the Seyfert nucleus and an inner ring of intense star formation. The forbidden O III 5007-A image shows that the high-excitation gas is elongated perpendicularly to the direction of the bar, and reveals a bright compact object at about 40 arcsec NE of the nucleus which is undetectable in the broadband images. This object is interpreted as a dwarf young H II galaxy. The optical, near-IR, and FIR results show clear evidence that the nuclear and circumnuclear regions have composite and complex structure: a variable Seyfert 1 nucleus embedded in an intense and dusty star formation. environment.

Lipari, Sebastian↗
NASA NTRS1990

Spectral synthesis in the ultraviolet. III - The spectral morphology of normal stars in the mid-ultraviolet

The morphology of 218 mid-UV spectra of stars ranging from O through K in spectral type is examined. Several new line and continuum indices are defined and their usefulness as temperature, luminosity, and metallicity discriminants is discussed. Mid-UV stellar continua are found to be markedly affected by abundance. A UV excess, delta(2600-V), is computed which is more sensitive by a factor of 10 to (Fe/H) than is delta(U-B). The relative strength of spectral lines in the mid-UV is not as strongly affected by abundance. Mid-UV spectra are much more sensitive to the temperature of the stellar population than to either metallicity or the dwarf/giant ratio. Mg II 2800 shows unexpected behavior, displaying no sensitivity to abundance for cool stars and a reversed sensitivity in FG dwarfs such that metal-poor stars have stronger Mg II strengths at the same temperature than more metal-rich stars.

Fanelli, Michael N.↗